1. Field of the Invention
The present invention relates to nanoparticle formed papers and nanoparticle deposition into fiber mats/preforms, their polymeric composites, and methods of their production and articles made therefrom.
2. Description of the Prior Art
With the soaring cost of fuels and other energy sources, innovative light weight materials that can provide high structural strength for aerospace, energy, transportation, and construction applications will benefit from a rapidly expanding market. Nanomaterials, and in particular, nanoparticle reinforced composites are one of the best solutions for these applications. The market potential of nanomaterials is enormous and Business Week recently stated that current products containing nanomaterials were valued at $26.5B. Nanotechnology is projected to have a $1 trillion impact on the U.S. economy by the year 2015.
Polymer/nanoparticle composites have been extensively studied since the 1990s. Because of the nanoscale dispersion and high aspect ratio of nanoparticles, polymer nanocomposites exhibit light-weight, dimensional stability, heat and flame resistance, barrier properties, and improved modulus and strength with far less reinforcement loading than conventional composites. While nanoparticles reinforce the polymer matrix, the loading of nanoparticles in polymer nanocomposites is often limited due to dispersion issues. Thus, mechanical properties of polymer nanocomposites are relatively low compared with those of highly loaded conventional fiber-reinforced plastics (FRPs with fiber loading >50 wt. %).
Over the last 15 years, substantial R&D efforts have been directed to develop methods that can prepare well-dispersed nanoparticles to form high performance nanocomposites. Approaches to incorporating nanoparticles into composite materials include premixing nanoparticles into a thermoplastic polymer matrix to form compounded pellets and forming a pre-preg thin film using a thermoset polymer resin. These approaches provide a relative improvement in properties over unmodified materials, but are limited to low nanoparticle loading and poor control of nanoparticle dispersion. For thermoset pre-pregs, limited shelf life is also a major drawback.
In recent years, researchers have developed ways to prepare nanoparticle thin films/papers but most of them are applicable only to carbon nanotubes (CNTs), i.e. ‘buckypaper’. Some use a paper making process, via the filtration of CNT suspensions in water or an organic solvent and then drying the resulting slurry; while others use more sophisticated fabrication methods such as Chemical Vapor Deposition (CVD), spin coating, drop casting, dip casting, and Langmuir-Blodgett deposition of nanoparticle suspension. All these methods have limitations such as high cost, poor film homogeneity and uniformity, low production rate and/or difficulty in dimensional control. There is significant market demand for a low-cost and mass-producible method that can produce high performance nanoparticle films/papers containing single or multiple nanoparticles to meet the requirements for safe nanomaterial handling and numerous industrial applications.
Fiber reinforced plastic (FRP) is the most widely used composite. In general, fibers are the principal load carrying members while the surrounding matrix keeps the fibers in the desired location and orientation and acts as a load transfer medium. Fiber reinforced plastics have low specific gravity, a high strength-to-weight ratio, and a high modulus-to-weight ratio. Fiber-reinforced plastics have good in-plane mechanical properties, determined by the reinforcing fibers, but the properties in the transverse and thickness directions defined by the characteristics of the matrix resin are much weaker. Under tension, compression, shear, or impact, failure of the polymer matrix may take place. It is highly desirable to incorporate nanoparticles into FRPs to remedy the aforementioned drawbacks. However, there aren't any low-cost fabrication methods that can bring the nanoparticles and FRPs together efficiently. Pre-mixing nanoparticles into the polymeric resins tends to increase the resin viscosity leading to long mold filling time in composite molding. Nanoparticles may also be filtered out by the fiber reinforcement causing non-uniform nanoparticle distribution in the molded composite.
Thermal and electric conductivities of composites are important properties for many structural applications. Next generation aerospace structures and wind blades could use more thermally and electrically conductive materials to judiciously direct heat flow and provide EMI shielding. The inherent poor thermal and electric conductivity of polymer composites, which are widely used in aerospace and wind blade structures, is not efficient in these applications. Many nanomaterials have been explored as candidates for improving the thermal and electric conductivity of polymer composites, including carbon nanotubes (CNTs) and carbon nanofibers (CNFs).